In an automobile a small size gas turbine engine is used that is provided with an annular combustion chamber. When the fuel is directly supplied to the combustion chamber, rapid combustion cannot be carried out because of an imperfect mixing of the fuel with air. This causes a large amount of NO.sub.x component to be generated, which is exhausted into the atmosphere.
To remedy this drawback, a gas turbine engine has already been provided that has an annular pre-mixing chamber arranged upstream of the annular combustion chamber. The annular pre-mixing chamber serves to obtain a well mixed air-fuel mixture which is supplied to the annular combustion chamber.